CN115448704B

CN115448704B - Forming method of ceramic blank

Info

Publication number: CN115448704B
Application number: CN202211127015.5A
Authority: CN
Inventors: 王士维; 刘文龙; 赵瑾; 刘娟; 毛小建; 章健
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2022-09-16
Filing date: 2022-09-16
Publication date: 2023-06-02
Anticipated expiration: 2042-09-16
Also published as: CN115448704A

Abstract

The invention relates to a method for forming a ceramic blank. The forming method of the ceramic body comprises the following steps: dispersing ceramic powder, isobutene and maleic anhydride copolymer in water to prepare water-based ceramic slurry, and controlling the solid content of the water-based ceramic slurry to be 40-60 vol%; and (3) injecting the obtained water-based ceramic slurry into a mold completely penetrated by microwave energy, then forming ceramic gel by spontaneous solidification under the action of microwave with power of more than 250 and W, and demoulding and drying to obtain a ceramic blank.

Description

Forming method of ceramic blank

Technical Field

The invention relates to a forming method of a ceramic blank, and belongs to the field of ceramic preparation.

Background

Compared with the traditional ceramic forming methods such as dry pressing, cold isostatic pressing and the like, the colloidal forming has obvious advantages in the aspect of preparing advanced ceramics with complex macroscopic structure and uniform microscopic structure. In 2011, yang Yan et al (Chinese patent publication No. CN 103130509A) invented spontaneous solidification molding, which uses a copolymer of water-soluble isobutylene and maleic anhydride to prepare a ceramic slurry having a solid content of more than 50vol%, and uses spontaneous gel solidification of the copolymer to obtain a ceramic body. The self-solidifying forming method has the advantages of small addition amount of organic matters, no toxicity, uniform biscuit microstructure and the like, and has been successfully applied to the preparation of structural ceramics (J.Mater.Res., 2014.29 (2): p.247-251.), foamed ceramics (J.Adv.Ceram., 2021.10 (4): p.852-859.), and transparent ceramics (J.Adv.Ceram., 2022.11 (4): p.582-588.). However, the slower gel speed requires about 18 hours to complete the gel cure, resulting in a wet blank containing about half the volume of moisture; the ceramic particles may be settled in the gel curing stage, so that the density distribution of the green body is uneven, and the green body is deformed or cracked by drying.

Disclosure of Invention

Aiming at the problems of slow gel solidification and long wet blank drying process existing in spontaneous solidification forming, the inventor adopts a method of microwave-assisted spontaneous solidification forming, namely, proper microwave power is adopted to accelerate the movement of ceramic particles, the movement of dispersing agent molecules and the rotation of polarized dipoles in the molecules, so that the probability of collision or contact between the molecules is increased, the association of hydrophobic groups is promoted, part of water in the ceramic wet blank is rapidly and uniformly discharged, the gel speed is greatly improved, and the uniformity of the biscuit is improved.

Specifically, the invention provides a forming method of a ceramic blank, which comprises the following steps:

dispersing ceramic powder, isobutene and maleic anhydride copolymer in water to prepare water-based ceramic slurry, and controlling the solid content of the water-based ceramic slurry to be 40-60 vol%;

and (3) injecting the obtained water-based ceramic slurry into a mold completely penetrated by microwave energy, then forming ceramic gel by spontaneous solidification under the action of microwave with power of more than 250W, and then demolding and drying to obtain a ceramic blank.

In the invention, firstly, the water-based ceramic slurry with low viscosity, good fluidity and 40-60 vol% of solid content is prepared by adding the copolymer of isobutene and maleic anhydride. The obtained slurry is subjected to vacuum degassing and then spontaneously solidified under the assistance of microwaves, and by applying proper microwave power (for example, 250-350W power is applied to a wet blank with the water content of 150 g), under the action of microwaves, the movement of ceramic particles, the movement of organic molecules of a dispersing agent and the rotation of polarized dipoles in the molecules are accelerated, the probability of collision or contact between the molecules is increased, the association of hydrophobic groups is promoted, the water (about 15%) in the wet blank of the ceramic is discharged, the gelation process is greatly shortened, and the ceramic biscuit with higher strength and uniform structure is obtained. In addition, in the subsequent drying process, the drying time is further shortened, and the problems of cracking and the like are avoided.

Preferably, when the mass of water contained in the water-based ceramic slurry is not more than 150g, the power of the microwave is 250 to 550W, preferably 300 to 400W;

when the water content of the water-based ceramic slurry exceeds 150g, the power of the microwaves is not less than 400W, preferably more than 550W. The power is mainly matched with the water content of the slurry, and otherwise, the wet blank is broken due to the fact that the temperature is too high.

Preferably, the ceramic powder is oxide ceramic powder, non-oxide ceramic powder, composite ceramic powder of oxide and non-oxide, preferably at least one of alumina powder, zirconia powder, yttria powder, silicon carbide powder, magnesia-alumina spinel powder and mullite powder;

preferably, the particle size of the ceramic powder is 100nm to 1 μm.

Preferably, the copolymer of isobutylene and maleic anhydride is an ammonified water-soluble copolymer of isobutylene and maleic anhydride; the addition amount of the isobutene and maleic anhydride copolymer is 0.1 to 1wt percent, preferably 0.3 to 0.5wt percent of the mass of the ceramic powder.

Preferably, the water-based ceramic slurry is vacuum degassed and then injected into a mold through which the microwave energy completely penetrates.

Preferably, the mould completely penetrated by the microwave energy is an organic glass mould, an alumina ceramic mould and a polytetrafluoroethylene mould; preferably, the relative dielectric constant of the material of the mold through which the microwave energy completely penetrates is less than 2.8.

Preferably, the atmosphere for spontaneous solidification is air, the temperature is 30-70 ℃, and the time is 10-40 min, preferably 10-30 min.

Preferably, the drying temperature is 15-40 ℃, the relative humidity is 30-80%, and the drying time is 8-48 hours.

In another aspect, the present invention provides a ceramic body prepared according to the above-described molding method.

In still another aspect, the invention provides a ceramic component, wherein the ceramic blank is subjected to presintering, glue discharging and sintering to obtain the ceramic component.

Preferably, the presintering and glue discharging temperature is 600-1100 ℃ and the time is 4-8 hours;

preferably, the sintering temperature is 1400-1850 ℃ and the sintering time is 2-8 hours.

Still preferably, the sintering schedule further includes: the temperature rising rate is 2-8 ℃/min within 1000 ℃; after 1000 ℃, the temperature rising rate is 1-2 ℃/min.

The beneficial effects are that:

according to the method, the gel curing time can be shortened from 18 hours to 15 minutes;

the method can discharge about 15% of water in the ceramic wet blank, and reduces the risks of subsequent drying deformation and cracking.

Drawings

FIG. 1 compares the gelation process of a microwave-assisted self-solidifying shaped alumina green body of example 1 with a self-solidifying shaped green body prepared in comparative example 1;

FIG. 2 is a photograph of the alumina green body formed in example 1;

FIG. 3 is a photograph of a 40mm diameter and 40mm thick alumina green body prepared in example 4;

FIG. 4 is a photograph of an alumina green body of 400mm in length, 50mm in width, and 10mm in thickness formed in example 5;

FIG. 5 shows the cross-sectional microstructures of the microwave-assisted self-setting alumina ceramic prepared in example 1 and the self-setting alumina ceramic prepared in comparative example 1, which are similar;

FIG. 6 is a photograph of the alumina ceramic molded in example 1;

FIG. 7 is a photograph of ceramic greenware molded at 600W in example 4, comparative example 3, and 700W in comparative example 3.

Detailed Description

The invention is further illustrated by the following embodiments, which are to be understood as merely illustrative of the invention and not limiting thereof.

In the invention, the ceramic slurry with low viscosity and high fluidity is prepared by dispersing ceramic powder by a dispersing agent, and the solid content of the slurry is controlled to be 40-60 vol% of the water-based ceramic slurry. The water-based ceramic slurry is subjected to vacuum degassing and then is subjected to spontaneous solidification molding under the assistance of microwaves, so that the gel speed is greatly improved, and a ceramic biscuit with good uniformity and high strength is obtained, so that uniform and complete ceramic is prepared by sintering.

The invention takes ceramic powder as raw material, and obtains ceramic blank with uniform microstructure and higher strength by microwave-assisted spontaneous solidification molding method. The system adopted by the invention is simple to operate, nontoxic and safe in microwave equipment. Is particularly suitable for preparing ceramic parts with large size and complex shape. The following illustrates exemplary methods for preparing ceramic bodies and ceramics by microwave-assisted spontaneous solidification molding.

Dispersing ceramic powder, isobutene and maleic anhydride copolymer in water (deionized water), and mixing to obtain water-based slurry with solid content of 40-60 vol%. The mixing mode can be planetary ball milling, ball milling stirring or ultrasonic mixing. Wherein the copolymer of isobutene and maleic anhydride is an ammonified water-soluble isobutene maleic anhydride copolymer, the specific commercial trade mark is ISOBAM 600AF or ISOBAM 104, and the addition amount can be 0.1-1 wt%, preferably 0.3-0.5 wt% of the ceramic powder. In an alternative embodiment, the ceramic powder is an oxide ceramic powder, a non-oxide ceramic powder, or a composite ceramic powder, preferably at least one of alumina powder, zirconia powder, yttria powder, silicon carbide powder, magnesia-alumina spinel powder, mullite powder; preferably, the particle size of the ceramic powder is 100nm to 1 μm. As one example, deionized water, isobutylene and maleic anhydride copolymers and ceramic powders are ball milled and stirred to obtain a water-based ceramic slurry. The solid content of the slurry is 40-60 vol%, the content of the copolymer of isobutene and maleic anhydride is 0.1-1 wt%, the stirring time is 0.5-1.5 h, and the stirring rotating speed is 200r/min.

Preparing a ceramic blank with uniform microstructure. Injecting the water-based ceramic slurry into an organic glass solvent and applying microwave power according to the mass of water contained in the sample, wherein when the mass of water contained in the wet blank is not more than 150g, the water-based ceramic slurry is preferably 300-400W; when the moisture content of the wet preform exceeds 150g, the microwave power may be preferably 400W or more, and preferably more than 550W. The movement of ceramic particles, the movement of dispersing agent molecules and the rotation of polarized dipoles in molecules are accelerated under the action of microwaves, so that the probability of collision or contact between the molecules is increased, the association of hydrophobic groups is promoted, the uniform dehydration of wet blanks is accelerated, the spontaneous solidification forming is greatly promoted, and after solidification, the ceramic blanks are obtained through demoulding and drying. If the microwave power is too high, when the temperature of the ceramic wet blank is too high, water can boil to generate large steam pressure so as to lead the blank to be broken, and the obtained blank forms cracks. If the microwave power is small, the gel speed will slow down. Taking 150g of water content as an example, if microwave power is applied to the green body to be more than 550W, the wet green body is cracked under the action of microwaves, and the obtained green body forms cracks. If the microwave power is applied less, the gel speed will slow down. Wherein the mould completely penetrated by the microwave energy is an organic glass mould, an alumina ceramic mould, a polytetrafluoroethylene mould and the like; wherein, the relative dielectric constant of the material of the die is less than 2.8. In an alternative embodiment, the atmosphere for spontaneous solidification is air at a temperature of 30-70℃for a period of 10-40 min (also microwave time). After vacuum degassing the water-based ceramic slurry, it is poured into an organic glass container. The vacuum degassing time can be 1-5 min. As an example, the water-based ceramic slurry is degassed for 1-5 min under vacuum condition, then injected into a mold completely penetrated by microwave energy, and the slurry is rapidly gelled to form a ceramic wet blank under the auxiliary action of microwave, wherein the microwave power is 250-550W, and the microwave time is 10-40 min. And demolding and drying the obtained wet blank to obtain the ceramic biscuit with uniform microstructure.

As a detailed example of a method of molding a ceramic body, the method includes the steps of: (1) Preparing a water-based ceramic slurry containing 0.1 to 1wt.% of a copolymer of isobutylene and maleic anhydride, the solid content of which is 40 to 60 vol.%; (2) Injecting the water-based ceramic slurry into a mold completely penetrated by microwave energy after vacuum degassing, and performing rapid spontaneous solidification and molding under the action of microwave, wherein the power of the microwave is 250-550W, and the microwave time is 10-40 min; (3) And demolding and drying the wet blank subjected to microwave-assisted spontaneous solidification forming to obtain the ceramic biscuit.

And (3) discharging the adhesive and sintering the ceramic biscuit to obtain the ceramic component. Wherein the temperature of presintering and glue discharging is 600-1100 ℃ and the time is 4-8 hours. The sintering temperature is 1400-1850 ℃ and the sintering time is 2-8 hours. The sintering system is that the temperature rising rate is 2-8 ℃/min at 1000 ℃; after 1000 ℃, the temperature rising rate is 1-2 ℃/min.

In general, ceramic powder, isobutylene and maleic anhydride copolymer are dispersed in water, water-based ceramic slurry with low viscosity, good fluidity and 40-60 vol% of solid content is obtained by mixing, then a mold which is completely penetrated by microwave energy is injected into a commercial microwave oven, the movement of ceramic particles and dispersing agent molecules and the rotation of polarized dipoles in the molecules are accelerated under the assistance of microwave of more than 250W, the probability of collision or contact between the molecules is increased, the association of hydrophobic groups is promoted, and the ceramic wet blank can be rapidly and uniformly dehydrated, so that ceramic gel is rapidly and uniformly cured in situ to form the ceramic gel, the strength capable of demolding is reached in about 15min, the curing speed is about 72 times of that of the gel at the conventional room temperature, and then the ceramic blank is obtained by demolding and drying.

The present invention will be further illustrated by the following examples. It is also to be understood that the following examples are given solely for the purpose of illustration and are not to be construed as limitations upon the scope of the invention, since numerous insubstantial modifications and variations will now occur to those skilled in the art in light of the foregoing disclosure. The specific process parameters and the like described below are also merely examples of suitable ranges, i.e., one skilled in the art can make a suitable selection from the description herein and are not intended to be limited to the specific values described below. The ammonified water soluble isobutylene and maleic anhydride copolymers referred to in the examples below are specifically commercially available under the designation ISOBAM 600AF or ISOBAM 104.

Example 1:

(1) And (3) preparing slurry: taking high-purity alumina powder with the median particle diameter of 450nm (purity is more than 99.9%) as a raw material, taking deionized water as a solvent, and adding 0.2wt.% of ISOBAM 600AF and 0.1wt.% of ISOBAM 104 as dispersing agents and gelling agents; preparing uniformly dispersed ceramic slurry with solid content of 50vol.% by stirring and ball milling;

(2) Shaping a biscuit: injecting the slurry into a mold (made of plastic mold such as organic glass or Teflon) with microwave energy of 95mm×30mm×15mm for microwave-assisted spontaneous solidification molding (water content is about 20% of the slurry weight, about 150 g), and applying microwave power of 300W for 15min;

(3) Drying the biscuit: demolding the biscuit, and drying in a constant temperature and humidity box with the temperature of 25 ℃ and the relative humidity of 85 percent for 36 hours;

(4) Sintering ceramics: firstly, preserving the heat of the dried biscuit at 800 ℃ for 6 hours to perform presintering and glue discharging, and then heating at a temperature of 1000 ℃ at a heating rate of 5 ℃/min; heating to 1550 ℃ at a heating rate of 2 ℃/min at 1000 ℃ and preserving heat for 6h;

(5) Sample processing: the sintered ceramic is complete and has no deformation, and is processed into 36mm multiplied by 4mm multiplied by 3mm sample bars by cutting and polishing;

(6) Intensity test: the strength of the ceramic was measured using a universal tester and was 464MPa.

Example 2:

the preparation process in this example 2 is similar to that of example 1, except that: the powder used was a water-repellent treated yttria powder of median particle size 800nm, with 0.2wt.% of ISOBAM 104 and 0.3wt.% of ISOBAM 600AF as dispersants. The sintered ceramic has transparency, and the sample linear transmittance is up to 80%.

Example 3

The preparation process in this example 3 is similar to that of example 1, except that: the powder used was a high purity alumina powder with a median particle size of 200nm, to which 0.3wt.% of ISOBAM 600AF was added as a dispersant. The sintered ceramic has translucency. The sample has a linear transmittance of 50% at 600 nm.

Example 4

The preparation process in this example 4 is similar to that of example 1, except that: a mold with a diameter of 40mm and a height of 40mm, through which the microwave energy completely penetrated (the water content of the injected slurry was also 150g, a plurality of mold samples were put in, and the total amount of slurry was unchanged). The prepared thick sample biscuit has uniform microstructure and no deformation and cracking after sintering.

Example 5

The preparation process in this example 5 is similar to that of example 1, except that: 400mm by 50mm by 10mm microwave energy fully penetrated mold (moisture content also 150 g). The prepared large sample biscuit has uniform microstructure and no deformation and cracking after sintering.

Example 6

The preparation process in this example 6 is similar to that of example 1, except that: the microwave power applied was 250W and the microwave time was 20min.

Example 7

The preparation process in this example 7 is similar to that of example 1, except that: the microwave power applied was 400W and the microwave time was 13min.

Example 8

The preparation process in this example 8 is similar to that of example 1, except that: the microwave power applied was 550W and the microwave time was 10min.

Example 9

The preparation process in this example 9 is similar to example 5, except that: (1) The size of the mould through which the microwaves completely penetrate is 95mm by 30mm by 15mm, twice the volume of slurry is injected, and the water content reaches 300g. (2) The microwave power applied was 600W and the microwave time was 25min.

Example 10

The preparation process in this example 10 is similar to that of example 9, except that: the microwave power applied was 400W and the microwave time was 30min.

Comparative example 1

The preparation process in this comparative example 1 is similar to that of example 1, except that: no microwaves are applied during the molding and spontaneously solidify in a room temperature environment, which takes 18 hours.

Comparative example 2

The preparation process in this comparative example 2 is similar to that of example 1, except that: the microwave power applied by the spontaneous solidification forming is 600W, 700W and 800W respectively. At the high power, the blank may crack before 15min, and it is difficult to form a complete wet blank. Cracking of the ceramic green body occurs during the curing process because the microwave power is too high, which results in too high a temperature of the moisture in the ceramic green body, rapid boiling of the moisture, and high steam pressure to fracture the green body.

Comparative example 3

The preparation process in this comparative example 3 is similar to example 4, except that: the applied microwave power was 600W or 700W, respectively. At the high power described above, the blank would crack before 15 minutes, making it difficult to form a complete wet blank, see fig. 7.

FIG. 1 compares the gel strength change of the wet alumina blank obtained by microwave-assisted spontaneous coagulation molding in example 1 and the gel obtained by spontaneous coagulation molding in comparative example 1, and shows that the gel strength of the wet alumina blank is about 1/72 of the original gel strength obtained by microwave-assisted spontaneous coagulation molding in example 1, and the gel strength of the wet alumina blank is about 45kPa at room temperature for 18 hours, and the gel strength of the wet alumina blank is about 45kPa for 15 minutes.

Fig. 2 is a photograph of the alumina greenbody formed in example 1, from which it is known that the microwave-assisted spontaneous solidification formed greenbody has a uniform and complete microstructure.

FIG. 3 is a photograph of an alumina green body having a diameter of 40mm and a thickness of 40mm prepared in example 4, and it can be seen that microwave-assisted spontaneous solidification molding successfully prepared a thick ceramic green body.

FIG. 4 is a photograph of an alumina green body of 400mm in length, 50mm in width and 10mm in thickness formed in example 5, and it can be seen that microwave-assisted spontaneous solidification forming successfully produced a large-sized ceramic green body.

Fig. 5 shows the cross-sectional microstructures of the alumina ceramic prepared by microwave-assisted spontaneous solidification molding in example 1 and the spontaneous solidification molding alumina ceramic prepared in comparative example 1, and shows that the microstructures are similar, and it is also demonstrated that samples with similar properties are prepared and the time cost is greatly reduced under the condition of microwave-assisted spontaneous solidification molding.

Fig. 6 is a photograph of the alumina ceramic molded in example 1, and it can be seen that the microwave-assisted spontaneous solidification molding succeeded in producing the ceramic.

Claims

1. A method of forming a ceramic body, comprising:

dispersing ceramic powder, isobutene and maleic anhydride copolymer in water to prepare water-based ceramic slurry, and controlling the solid content of the water-based ceramic slurry to be 40-60 vol%; the ceramic powder is oxide ceramic powder, non-oxide ceramic powder, oxide and non-oxide composite ceramic powder; the copolymer of isobutene and maleic anhydride is an ammonified water-soluble copolymer of isobutene and maleic anhydride; the addition amount of the copolymer of isobutene and maleic anhydride is 0.1-1 wt.% of the mass of the ceramic powder;

injecting the obtained water-based ceramic slurry into a mold completely penetrated by microwave energy, then forming ceramic gel by spontaneous solidification in air at 30-70 ℃ for 10-40 min under the action of microwave with power more than 250W, and then demolding and drying to obtain a ceramic blank;

when the mass of water in the water-based ceramic slurry is not more than 150g, the power of the microwaves is 250-550W;

when the water content of the water-based ceramic slurry exceeds 150g, the power of microwaves is more than or equal to 400W.

2. The molding method according to claim 1, wherein the power of the microwaves is 300 to 400W when the mass of water contained in the water-based ceramic slurry is not more than 150 g;

when the water-containing mass of the water-based ceramic slurry exceeds 150g, the power of the microwaves is greater than 550W.

3. The molding method according to claim 1, wherein the ceramic powder is at least one of alumina powder, zirconia powder, yttria powder, silicon carbide powder, magnesia-alumina spinel powder, and mullite powder;

the particle size of the ceramic powder is 100 nm-1 mu m.

4. The molding method according to claim 1, wherein the amount of the copolymer of isobutylene and maleic anhydride added is 0.3 to 0.5wt.% based on the mass of the ceramic powder.

5. The molding method as claimed in any one of claims 1 to 4, wherein the water-based ceramic slurry is vacuum deaerated and then injected into a mold through which microwave energy completely penetrates.

6. The molding method as claimed in any one of claims 1 to 4, wherein the mold completely penetrated by microwave energy is a plexiglass mold, an alumina ceramic mold, a polytetrafluoroethylene mold.

7. The molding method of claim 6, wherein the material of the mold through which the microwaves completely penetrate has a relative dielectric constant of less than 2.8.

8. The molding method according to any one of claims 1 to 4, wherein the self-solidifying molding is performed for a time of 10 to 30 minutes.

9. The molding method according to any one of claims 1 to 4, wherein the drying temperature is 15 to 40 ℃, the relative humidity is 30 to 80%, and the time is 8 to 48 hours.

10. A ceramic body prepared according to the molding method of any one of claims 1-9.

11. A ceramic component characterized in that the ceramic body of claim 10 is subjected to presintering, glue discharging and sintering to obtain the ceramic component;

the presintering and glue discharging temperature is 600-1100 ℃ and the time is 4-8 hours;

the sintering temperature is 1400-1850 ℃ and the sintering time is 2-8 hours.